The study reveals understanding of a basic physical property of charged particles in microgravity

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A pattern of clustering and clustering of positively and negatively charged colloidal particles. m is the association number. Credit: Nuclear Science and Technology Organization of Australia (ANSTO)

A study conducted by a group of scientists from Nagoya City University (NCU), Japan Space Forum (JSF), Advance Engineering Services (AES), Japan Aerospace Exploration Agency (JAXA) and ANSTO has revealed a clustering of charged particles in the environment of microgravity of the International Space Station (ISS), with implications for the development of photonic materials, improved medicines and a range of new and innovative materials that depend on the mixing of two or more charged particles.

The experimental study, published in npj Microgravityand conducted on the ISS, determined how charged sub-micron colloidal particles interact in the presence and absence of Earth’s gravity.

“Many chemical and physical phenomena rely heavily on understanding how two particles interact with each other, especially charged particles,” said Jitendra Mata, lead scientist and co-author of ANSTO.

“The best example is when colloidal particles form tetrahedral clusters, commonly known as diamond lattices, which are essential in the production of photonic materials. Controlling the self-assembly of colloidal particles allows us to build a new material that can be used in photonics, optoelectronics, sensing and clinical diagnostics”.

Even the slightest sedimentation and gravitational convection on Earth are known to affect particle interactions and their arrangement in a colloid. This hinders important knowledge of the effect of charging.

This knowledge can also help design better drug formulations, which will have higher self-life and better efficacy.

In this study, the researchers selected the lightest and heaviest positively and negatively charged particles. The polystyrene particles are only as heavy as the aqueous medium containing them, and the titania particles are about three times as heavy as the medium.

The samples were immobilized in a gel after their interaction so that they could be brought back to Earth for various experiments.

(d) Sample bag, consisting of two tetra-pack compartments connected by an unbreakable separator (e) The UV irradiation system. (f) Sample (Titania #23) returned to the ground and (g) Cross section of the gel-fixed space sample and the ground sample. Credit: Nuclear Science and Technology Organization of Australia (ANSTO)

The research revealed that clusters formed by lighter particles in space are 50% larger than clusters formed on earth. This is a groundbreaking discovery as it was not intended for lighter particles.

For heavy particles, such as titania, an electrostatic interaction and formation of clusters has also been confirmed which is not possible at all on Earth.

This study also required an engineering marvel, in terms of designing the experimental setup for mixing samples in space and the immobilization of these samples after mixing.

After the design was shortlisted by JAXA, the team worked closely with multiple organizations to build a custom setup that could allow for mixing and immobilization of gel clusters using LED-UV light.

Two sets of samples were prepared in Japan; one was sent to the ISS using a Falcon (Space-X) rocket and a Dragon SpX-19 transporter and the other was used in a ground experiment. The ISS crew used the prescribed procedure to mix the samples before curing them with LED-UV light. After spending more than a year in space, the samples were brought back to Earth and sent to different institutes for analysis.

A batch of samples arrived at ANSTO, home to two state-of-the-art reactor-based instruments: QuokkaSmall Angle Neutron Scattering (SANS) and KookaburraUltra Small Angle Neutron Scattering (USANS).

‘Quokka and Kookaburra are unique tools that provided unrivaled insight into cluster structure, which is very difficult to study with other techniques. With SANS and USANS contrast variation, it was possible to gain insight into individual components in the clustering process.’ Dr. Mata said.

The combined data from these two instruments provided important insight into the structural morphology and charge-charge interaction of ~1 nm colloidal particles at 10 m, without compromising the crystalline environment of the samples. The study also features many other techniques including mathematical modeling and simulations.

More information:
Hiroyuki Miki et al, Clustering of Charged Colloidal Particles in the Microgravity Environment of Space, npj Microgravity (2023). DOI: 10.1038/s41526-023-00280-5

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